1. Field of the Invention
This invention relates to heat pumps and more particularly to control means for automatically reversing refrigerant flow to provide heating, cooling or defrosting.
2. Description of the Prior Art
It is well known in the art that heat pumps include indoor and outdoor coils or heat exchangers connected in a closed refrigerant circuit. Refrigerant is circulated through the coils by a compressor which draws the refrigerant from one coil, compresses the refrigerant and delivers the compressed refrigerant to the other coil where it is condensed and flows through expansion device such as a capillary tube or expansion valve, to the first coil for evaporation. The system typically includes a changeover valve for periodically reversing the refrigerant flow so that the unit operates on a cooling cycle or a heating cycle. Typically, a four-way valve is employed in foregoing system to reverse the cycles. To increase the efficiency of the heat pump system where the same heat transfer coil is selectively used as a condenser or an evaporator, the coils are provided with a plurality of heat transfer circuits. These circuits are arranged to be in a series when the coil operates as a condenser and in parallel when the coil operates as an evaporator. To enable this system to operate under the reverse cycle principle a number of check valves are utilized to direct the refrigerant flow through the coils in series when the coil is functioning as a condenser and to direct flow through the circuits in parallel when the coil is functioning as an evaporator. A number of check valves are also arranged in the circuit to permit refrigerant flow from each heat transfer circuit connected in the coil in parallel when the coil is operating as an evaporator, to a suction line of the compressor. Utilization of large numbers of valves requires a number of mechanical joints which must operate under conditions of relatively high pressures and temperatures. It is therefore desirable to eliminate these check valves to the extent possible.